In a recording device (disk drive unit) having a disk-shaped recording medium in which servo information is recorded, read operation and write operation are performed by moving a head for use in reading and writing data on a plurality of tracks arranged concentrically on a disk-shaped recording medium (disk). Because it is important to move the head along the center of each track, servo information is employed so as to position the head accurately.
In such a sector servo system, the servo information is recorded on the disk surface radially in a radius direction perpendicular to each track. A portion in which the servo information is recorded is referred to as a servo gate. In the servo information, there are included a track number, a servo gate number denoting the location number of the servo gate assigned on a track-by-track basis, and a burst signal for detecting deviation of the head position from the center of the track.
In the conventional read or write operation for a disk drive unit having the aforementioned servo information, whenever the head transits on the servo gates during the read/write operation, it is checked whether the head position does not deviate from the center of the track, based on the servo information. By use of an interruption, a check result is reported to a processor which totally controls the disk drive unit.
When the head position deviates from the center of the track (hereafter this deviation is referred to as ‘off-track’), this may possibly corrupt data on a track other than the object track. To prevent such an undesirable situation, the processor identifies the check result preferentially to perform an interruption processing. This causes temporarily suspension of normal control operation. When such an occurrence of the off-track is identified, the processor suspends the ongoing read/write operation.
Meanwhile, with the increase of both data size and application size handled by users, and with the increase of speeds of peripheral units and a central processing unit, there has been demanded a disk drive unit which is larger in capacity and higher in performance than before.
In order to develop a disk drive unit having a larger recording capacity with the unit size unchanged, a high-density disk drive unit has been achieved by decreasing a space between the tracks (track pitch). As a result of a decreased track pitch, there becomes an increased possibility of the data corruption caused by the head accidentally handling a data on a track neighboring an object track. In order to prevent such a malfunction, it has been required for the head to be located with more accuracy, as well as the off-track check be performed more strictly. As a result, the number of servo gates has been increased.
Also, in order to develop a high-performance disk drive unit, there has been an improvement in a data amount to be read out per a unit time by rotating the disk at higher speed. As a result of high-speed disk rotation, there has been an increased number of head transitions across the servo gates in a unit time, as compared to previous cases.
As mentioned above, a high-density disk rotating at high speed has brought about an increase of the servo gates, as well as an increase in the number of head transitions across the servo gates in a unit time. As a result, the number of interruptions against the processor has also been increased. The increased number of interruptions has produced an increased load of the processor, and an increased number of interruptions in the normal control. This has caused a problem of increasing a delay produced in processing other than the interruption processing.